Combined oxidation and absorption of NOx by an ionic liquid tandem process

A method for removing NOx gasses by an absorption process and conversion of NOx to nitric acid (HNO3) in the presence of oxygen and water, wherein the NOx gasses comprise NO, NO2, N2O3 and N2O5, comprising:

• a) oxidizing nitric oxide (NO) to nitrogen dioxide (NO2) and other HxNyOz species with an ionic composition catalyst at an oxidation temperature below the decomposition temperature of the ionic composition catalyst, wherein the oxidation temperature is between 80 and 120° C., thereby forming an oxidized gas mixture, wherein x, y and z are integers in the ranges x=0-1, y=1-2, z=1-5, and
• b) absorbing NO2 and other HxNyOz species generated in step a) and converting the absorbed NO2 and other HxNyOz species to nitric acid (HNO3), wherein the absorption and conversion occurs in a medium in the presence of oxygen and water at a temperature between 30 and 80° C. but at a temperature that is lower than the oxidation temperature in step a), wherein the nitric acid (HNO3) accumulates in the medium, and wherein the ionic composition catalyst comprises one or more ionic compounds.